1. Field of the Invention
The present invention relates generally to accelerometers and more particularly pertains to accelerometers in which a proof mass is constrained by a combination of electromagnetic and elastic supports.
2. Description of the Prior Art
Electromagnetic force rebalance accelerometers are well known. In this type of accelerometer, a proof mass is constrained by force generated in a current-carrying conductor or coil located in a magnetic field. Such accelerometers have typically been built as single-degree-of-freedom instruments. Thus, three such accelerometers are required to be included in an inertial navigation system. Such a system obviously tends to be more costly and complex than would be one which performed its function using fewer instruments. Furthermore, in such a single-degree-of-freedom accelerometer, a structural member of substantial size and mass is typically required to center and maintain the alignment of the coil at the full rated acceleration of the instrument in two of the three directions. This structural member, however, tends to augment the null drift or bias uncertainty of the accelerometer, primarily because of dimensional changes which result from ambient temperature variations. In order to reduce this bias uncertainty, accelerometers intended for use in high-performance navigation systems are typically provided with temperature control elements for holding the temperature-sensitive portions of the instrument at a relatively constant temperature. The need for temperature control in accelerometers is another factor tending to increase the cost and complexity of inertial navigation systems.